Human fecal contamination represents a serious health hazard for the transmission of waterborne diseases such as typhoid fever, cholera, and hepatitis A. Therefore, sensitive measurements of water supplies and food handling processes for fecal microorganism are of great value in identifying dangerous human fecal contamination and tracking its source. The development of such a rapid, portable, human fecal contamination biosensor is the overall goal of this program. The Specific Aims of this six-month Phase I program are: 1) Determine the sensitivity, specificity, and reuse of an optical fiber based evanescent wave DNA hybridization assay using synthetic oligos, 2) Determine the sensitivity and specificity of the optical fiber hybridization assay targeting Bacteroides and Prevotella rRNA sequences using human and animal fecal samples, and 3) Determine the stability and reproducibility of the assay components for long-term use.